A belt-driven continuously variable transmission adapted to change a speed ratio continuously using a driving belt is known in the art. The belt-driven continuously variable transmission is comprised of a primary pulley and secondary pulley arranged in parallel fashion, and a driving belt running on those pulleys to transmit power therebetween. Each of the pulleys is individually comprised of a fixed sheave integrated with a rotary shaft, and a movable sheave fitted onto the rotary shaft while being allowed to reciprocate thereon. A conical face is formed on an inner face (as will be called a “pulley face” hereinafter) of each sheave to be opposed to each other. Therefore, the driving belt being contacted to the pulley face transmits the power frictionally therebetween.
When transmitting a torque frictionally between the driving belt and the pulley, the movable sheave has to withstand a reaction force from the driving belt against a thrust force pushing the movable sheave, and when the torque being transmitted is increased, the reaction force is also increased. In this situation, the movable sheave is flexurally deformed by the reaction applied thereto. Consequently, a friction between the driving belt and the sheaves may be reduced and a speed ratio may be varied. Japanese Patent Laid-Opens Nos. 2010-181017 and 2000-170859 disclose belt-driven continuously variable continuously variable transmissions adapted to prevent a flexural deformation of the movable sheave. Specifically, Japanese Patent Laid-Open No. 2010-181017 discloses a belt-driven continuously variable continuously variable transmission in which a thrust force is applied to an outer circumferential portion and to an inner circumferential portion of the movable sheave. Meanwhile, Japanese Patent Laid-Open No. 2000-170859 discloses a belt-driven continuously variable continuously variable transmission in which a thrust force is applied to a portion of the movable sheave radially outside of a contact point at which the driving belt moved to the maximum diameter position comes into contact therewith.
Meanwhile, the flexural deformation of the movable sheave caused by a load applied thereto from the driving belt may be reduced by thus modifying the belt-driven continuously variable continuously variable transmission. However, the movable sheave is fitted onto the rotary shaft integrated with the fixed sheave, in other words, the rotary shaft of the fixed sheave is inserted into a hollow shaft of the movable sheave. That is, a slight clearance remains inevitably between an inner surface of the hollow shaft of the movable sheave and an outer surface of the rotary shaft of the fixed sheave. Therefore, the movable sheave may be inclined by a reaction force from the driving belt thereby reducing the friction force and changing a speed ratio unintentionally.